High performance carbon nanotube transistors have been demonstrated, outperforming the silicon (Si) counterpart. Carbon nanotubes are therefore one of the leading candidates for a future, post-Si, high performance logic technology.
However, for the carbon nanotube devices to be competitive with their Si counterparts, the carbon nanotubes need to be placed at a sufficiently high density. Several approaches exist for carbon nanotube placement, but none is able to deliver carbon nanotube density in the required range in large scale. For instance, some of the approaches provide for a high carbon nanotube density, but there is no pathway to scale up the process. See, for example, Han et al., “DNA-linker-induced surface assembly of ultra dense parallel single walled carbon nanotube arrays,” Nano letters, vol. 12, issue 3, pgs. 1129-1135 (February 2012); and Wu et al., “Self-Assembly of Semiconducting Single-Walled Carbon Nanotubes into Dense, Aligned Rafts,” Small, Vol. 9, Issue 24, pgs. 4142-4148 (December 2013). Further, with these techniques the carbon nanotubes are not aligned. Other approaches—such as chemical vapor deposition (CVD) on crystal steps of annealed quartz or sapphire—achieve good alignment of the carbon nanotubes, however the density is low. Further, these approaches result in mixed carbon nanotube types (semiconducting and metallic). Repeating the process to increase density only serves to increase the amount of undesirable metallic carbon nanotubes present.
The controlled placement and arrangement of carbon nanotubes on a substrate was demonstrated, for example, in Park et al., “High-density integration of carbon nanotubes via chemical self-assembly,” Nature Nanotechnology 7, 787-791 (October 2012) (hereinafter “Park”); and U.S. Patent Application Publication Number 2014/0363643 by Afzali-ardakani et al., entitled “Surface-Selective Carbon Nanotube Deposition Via Polymer-Mediated Assembly.” These approaches, however, have a limited resolution which is a roadblock to scalability.
Thus, scalable techniques for producing high-density, well-aligned, semiconducting carbon nanotubes would be desirable.